AN205561
F²MC-8FX Family MB95200 Series 8-Bit Microcontroller BLDC Motor Back EMF
120° Driver Method
Associated Part Family: MB95200 Series
This document describes the BLDC (Brushless DC) motor back EMF 120° driver method used by MB95330H Series.
Contents
1
2
3
4
Introduction .................................................................. 1
Background Description .............................................. 1
2.1 Description of Multi-pulse Generator ................... 1
2.2 Back EMF Description ........................................ 5
Hardware Design Description ...................................... 8
3.1 System Block Diagram Description ..................... 8
3.2 Position Detection Resolver ................................ 9
Firmware Principles and Theory ................................ 11
4.1 Firmware Main Flowchart .................................. 11
4.2 Sensorless Startup ............................................ 12
4.3 Transition from Startup to Normal Run ............. 15
1
4.4 Normal Run ....................................................... 16
5 Notes on Using Back EMF Driver method ................. 20
5.1 Relationship between Driving Patterns and
Position Detection ..................................................... 20
5.2 Notes on Operation of DTTI Input Control ........ 20
5.3 Advantage or Disadvantage of Sensorless
Control ....................................................................... 20
6 Additional Information ................................................ 21
Document History............................................................ 22
Introduction
This document describes the BLDC (Brushless DC) motor back EMF 120° driver method used by MB95330H series
8-bit microcontroller.
2
Background Description
This section describes the multi-pulse generator (MPG) and back EMF 120° driver BLDC motor.
2.1
Description of Multi-pulse Generator
The multi-pulse generator consists of a 16-bit PPG timer, a 16-bit reload timer and a waveform sequencer. By using
the waveform sequencer, 16-bit PPG timer output signal can be directed to multi-pulse generator output (OPT5 to
OPT0) according to the input signal of multi-pulse generator (SNI2 to SNI0). Meanwhile, the OPT5 to OPT0 output
signal can be terminated by DTTI input in case of emergency. The OPT5 to OPT0 output signals are synchronized
with the PPG signal in order to eliminate the unwanted glitch.
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2.1.1
Block Diagram of Multi-pulse Generator
Figure 1. Block Diagram of Multi-pulse Generator
Figure 1 shows the block diagram of multi-pulse generator.

16-bit PPG Timer
The 16-bit PPG timer is used to provide the PPG signal for waveform sequencer. Details of 16-bit PPG timer are
described in Hardware Manual of MB95330H Series.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method

16-bit Reload Timer
The 16-bit reload timer is used to act as interval timer for waveform sequencer. Details of 16-bit reload timer are
described in Hardware Manual of MB95330H Series.

Waveform Sequencer
The waveform sequencer is the core of multi-pulse generator, which can generate various waveforms.
2.1.2
Registers of Multi-pulse Generator
Figure 2. Registers of Multi-pulse Generator
(Continued)
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
(Continued)
Figure 2 shows registers of multi-pulse generator. For more detailed information, please refer to Chapter 24 in
Hardware Manual of MB95330H Series.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
2.2
Back EMF Description
2.2.1
Back EMF Generation
Based on simple physical theory, when there is a relative motion between a conductor and a magnetic field, the
current will flow through the conductor and a potential difference is generated.
Figure 3. Motor Relative Motion by Potential Difference
Apply the same principle to a brushless DC motor and user can find the induced current on the phase coil which is
open.
Study the above situations and monitor the marker A and A’ in the “Before” and “After” respectively, user can
recognise the induced current and its direction.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
2.2.2
M o t o r C o m p l e t e R e vo l u t i o n
By applying the same analysis, below shows a motor rotating mechanism on the complete revolution.
Figure 4. Motor Rotating Mechanism on the Complete Revolution
By detecting the rising and falling edge of induced voltage on the opened phase coil terminal, communication can be
done electronically, it is the basic principle how sensorless control of brushless DC motor can work.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
2.2.3
Back EMF Modeling
In order to understand how the back EMF is useful in the implementation, it is important to study the 3 phase back
EMF modelling.
Figure 5. 3 Phase Back EMF Modelling
From the above explanation, we can see an important fact that the voltage on the opened terminal is equal to half of
the power supply VCC at zero crossing.
Therefore, in order to recognise the time of zero crossing, the voltage on the terminal of phase coil is compared with
the VCC/2. However, since the VCC is very high, VCC/2 level and the voltage from the terminal are scaled down to a
suitable level so that it can be fed to the comparator.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
3
Hardware Design Description
This section describes system hardware design.
3.1
System Block Diagram Description
The basic configuration of a sensorless controlled brushless DC motor system is shown below.
Figure 6. System Block Diagram
MB95330
The basic components are:

IGBT-IPM
IGBT-IPM (intelligent power module) consists of an IGBT model and a signal driver circuit. It is connected to the
MCU output port and 3 phase brushless DC motor.

Position resolver
This circuit consists of a simple potential divider and isolators. It captures the potential from phase coils and is
compared with a fixed voltage. Through the isolators are connected to the input port of MCU.

MB95330
Core of the sensorless control, which accepts output from position resolver and drives the IPM through the
isolators.

IPM power supply
IPM can supply current to its upper arms switches and lower arm switches.

Main power supply
Provides a stable high DC voltage to drive the motor or compressor.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
3.2
Position Detection Resolver
3.2.1
Position Detection Circuit Design
One of the critical circuitry is the position resolver; it must be very precise to differentiate a few micro-volt signals.
Figure 7. Position Detection Resolver Circuit Design

Comparators
Low offset type can give more precise position detection timing.
Practically, protection diode circuit for each input is used to avoid exceeding signal swinging.

Resistors
The resistors should be kept stable when temperature changes.
Low tolerance type should be used and the precision is at least 1%.
The precision of these resistors is critical to sensorless control.

Decoupling capacitors
PWM noise from the phase voltage should be decoupled before being fed to the MCU. Therefore, each
comparator input should build in a decoupling capacitor.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
3.2.2
P o t e n t i a l D i vi d e r
The high voltage on the terminal should be scaled down by a carefully designed potential divider circuitry.
Figure 8. 3 Phase Back EMF Potential Divider Circuitry
Above is the potential divider used in the implementation. Resistors with low tolerance and special values such as
523 Ω and 2.26 kΩ are used to realize a precise potential divider. Precision is very critical to the sensorless control,
an insufficient precision design generally leads to unstable startup.
U, V and W are connected to the 3 phase terminal. P is connected to the positive terminal of power supply, the
470 kΩ, 2.26 kΩ and 523 Ω resistors create a scaled down value of VCC/2.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4
Firmware Principles and Theory
The section describes firmware operation principles and theory.
4.1
Firmware Main Flowchart
When the rotor stops, the rotor position is unknown because of the missing of position sensor, so the back EMF
measurement does not work.
Figure 9. Flow Chart of Startup Motor Rotor
There are 2 stages before entering normal running status.

Sensorless startup
The rotor may rotate opposite to the desired direction for a short moment, or even very seldom fail to startup, in
this case, user can perform forced startup. Forced startup can be implemented easily by small code size and is
very suitable to control brushless DC compressor. User can try startup again by retry function when the
compressor starts abnormally.

Judgement of normal running state
This judgment algorithm ensures the compressor is running perfectly and is suitable to enter normal running.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.2
Sensorless Startup
4.2.1
S t a r t u p D r i vi n g P a t t e r n
Here is the driving pattern used for sensorless startup.
Figure 10. Driving Pattern Used for Sensorless Startup
Although the pattern is simple to be implemented, the sensorless startup is very reliable. The compressor always
starts up successfully without any retry.
A – B is the mask-off time which MCU external interrupts are disabled.
B – A’ is the time which MCU external interrupts are enabled.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.2.2
Back EMF Zero Crossing Detection
In sensorless startup, the back EMF generated at the very first moment is extremely small. Below is a captured
waveform showing the back EMF in the terminal and the scaled down VCC/2 level.
Figure 11. Back EMF Zero Crossing Detection
Back EMF zero crossing happens when the minimum point has a value lower than that of E/2.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.2.3
S t a r t u p Al g o r i t h m
There is a simple algorithm used in startup stage.
Figure 12. Simple Algorithm Used in Startup Stage

Change state
Change state when there is a back EMF zero crossing interrupt or a preset timer timeout. Preset timer value
ranges from 50 ms to 200 ms tested according to the compressor used.

Change to normal run
The state change is monitored for about 10 - 30 electrical cycles, if the deviation of the duration is not too much,
it is assumed the compressor is running smoothly.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.3
Transition from Startup to Normal Run
In the implementation, only the state change duration of last electrical cycle is considered.
Figure 13. Ensure Electrical Cycle’s Value of Startup to Normal Run
A simple formula below can be used to ensure the value of last 6 items does not exceed the smallest deviation value.
Tmax < k * Tmin
Where Tmin and Tmax are the minimum value and maximum value of the 6 items, k is a constant and the range of k
is from 5 to 10.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.4
Normal Run
4.4.1
D r i vi n g P a t t e r n
The normal-run consists of 12 different driving patterns and 6 different states. Below shows the relationship between
the driving patterns and the expected interrupts from the position detection circuit.
Marker explanation:
A
: position detection interrupts
B
: change state
C
: change chopping-arm
D
: position detection interrupt enable
A’
: next position detection interrupts
A – B: commutation delay
B – C: change arm delay
C – D: change arm mask-off period
Figure 14. Driving Pattern of Normal Run
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.4.2
Real Time Parameters
Some real-time parameters are very important in normal running status and are critical to the motor operation.
Figure 15. In Fact Drive Pattern of the Motor Operation

Commutation delay
It is the state change delay after the position detection interrupts.
This parameter depends on the characteristics of the target motor and current rotational speed.
0 to 30 electrical degrees are typical practical value.
This parameter usually used to fine the efficiency and torque at different speed.

Position detection mask
Position detect interrupt is masked off just after arm changes, an unwanted interrupt may happens at that time.

Position detection ready
Starting from that time, position detection interrupt is possible to interrupt the MCU.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
4.4.3
Ar m C h o p p i n g T e c h n i q u e
The use of arm chopping to capture rising or falling edge of back EMF is critical. Here describes how to capture rising
and falling edge of back EMF using appropriate chopping arm.

Rising edge detection
Lower arm chopping will cause the voltage on the opened terminal to exceed the middle reference level, and
generates a lot of unwanted interrupts, MCU input interrupt is masked off at this moment.
Upper arm chopping will cause the voltage on the opened terminal to exceed the middle reference level only
when the back EMF is really zero-crossing, it is a valuable instance to MCU.
Figure 16. Rising Edge Detection Waveform of Back EMF

Falling edge detection
Upper arm chopping will cause the voltage on the opened terminal to exceed the middle reference level, and
generates a lot of unwanted interrupts, MCU input interrupt is masked off at this moment.
Lower arm chopping will cause the voltage on the opened terminal to exceed the middle reference level only
when the back EMF is really zero-crossing, it is a valuable instance to MCU.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
Figure 17. Falling Edge Detection Waveform of Back EMF
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
5
Notes on Using Back EMF Driver method
The section describes notes on using BLDC motor Back EMF 120° Driver method.
5.1
Relationship between Driving Patterns and Position Detection
The relationship between the driving patterns and the expected interrupts from the position detection circuit varies
depending on BLDC motor, so user should first find the relationship of them, and then set registers in code.
5.2
Notes on Operation of DTTI Input Control
In system, the DTTI over current protection should be enabled. The OPT5 to OPT0 is fixed at the inactive level when
the low input level is placed at the DTTI pin.
Even while the output is fixed at the inactive level by the input of the DTTI pin, the timer keeps running, the position
detection function does not stop and the data transfer from the output data buffer register (OPDBR) to the output data
register (OPDR) is continued for waveform generation, but no waveform is output to the OPT5 to OPT0 pins.
5.3
Advantage or Disadvantage of Sensorless Control
5.3.1
Ad va n t a g e o f S e n s o r l e s s C o n t r o l
BLDC motor back EMF 120° driver is sensorless control. The system has no position sensor of hardware design. It
drives BLDC motor which has position sensor or position sensorless motor. As a result, the system debases difficulty
of hardware design.
5.3.2
D i s a d va n t a g e o f S e n s o r l e s s C o n t r o l
The system has no position, so user should calculate the back EMF to find current position of motor by position
detection triggered. As a result, the system increases operation of software design and increases difficulty of firmware
design.
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
6
Additional Information
For more information on Cypress MB95200 products, please visit following website:
http://www.cypress.com/MB95200
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
Document History
Document Title: AN205561 – F²MC-8FX Family MB95200 Series 8-Bit Microcontroller BLDC Motor Back EMF 120° Driver
Method
Document Number: 002-05561
Revision
ECN
Orig. of
Change
Submission
Date
**
-
CBZH
04/30/2009
Initial release
05/13/2009
Modify according Document Feedback
05/10/2016
Migrated Spansion Application Note MCU-AN-500042-E-11 to Cypress format.
*A
5266026
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CBZH
Description of Change
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MB95200 Series BLDC Motor Back EMF 120° Driver Method
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